I take it you tried this? If so then it did not help but made things worse. At least there was a huge spike in server earlier this day, guess that was you trying..
I just wonder why that router is such a crap.
Well if you just want to play with friends you can tell the server NOT to register at the master servers (sv_public 0) and tell your friends to connect manually by opening the console and using (connect IP:PORT) of your router/server..
Oh and maybe you can show us how your screen looks when having this thing open:
Maybe we misunderstand you or you did something wrong with the forwarding.. just to make sure.